Photocatalytic reduction of gaseous CO2 by water vapor without any additional sacrificial electron donors was studied on TiO2 P25 as photocatalyst. Formation of oxygen, hydrogen, C1–C4 hydrocarbons, as well as methanol, ethanol and acetone was observed under the high power UV-LED illumination. Complete photocatalyst deactivation was observed after 400 h of irradiation. The subsequent photocatalyst illumination in the oxygen containing atmosphere (air) resulted in its reactivation. Photocatalyst sample changed its color to yellow during the CO2 reduction process and turned back white after the reactivation by illumination in the presence of oxygen. On the basis of these observations conclusion was made that photocatalyst are deactivated because CO2 reduction sites are blocked by some reduction products which could be depleted by illumination in the oxygen containing atmosphere.